What bicycle crank arm length should I buy?

This is a question we get almost every day, so we wanted to briefly explain how to determine your crank arm length and why shorter, might be better for you.

Stock Crank Arm Lengths

Firstly, most of us are riding the crank length that came on our new bike off the showroom floor. And there is nothing at all wrong with that. Crank lengths on stock bikes lengthen as the bike size increases. By the way, you can usually find the crank length stamped on the inside of your crank near the pedal threads.

Why a Shorter Crank Arm Might be Better

Over the last 20 years or so, the triathlon world has been shortening their cranks. Why? Well, for the initial triathlon push, it was only for aerodynamics. The lower you can get on the bike, the more aerodynamic you are. However, most of us can only get so low! Take this easy at-home example:

1) More Aerodynamics

Stop pedaling at the top of your pedal stroke (12 o’clock) and bring your torso down to your flexibility maximum. Your honest flexibility maximum please. This can be replicated off-bike by locking your knees and bending forward at the waist. Consider this your maximum hip angle. Now the only way to get lower would be to push through this angle, risking injury and destroying your pedal stroke. Or…by shortening your crank arms! For example, at 12 o’clock, your foot now goes through the top at a lower point, and your torso can go lower with it. Great news! More aerodynamics!

2) Improved Kinetics

However, it turns out there are also kinetic benefits, which were the unexpected icing on the triathlon cake. The kinetic benefit for many with higher torso angles (limited flexibility) is satisfyingly, more 12 o’clock clearance, and subsequently, way more comfort.

Fortunately, we are now seeing shorter crank arm lengths finally seep into stock road, triathlon and MTB bikes.

Photo Credit: Nate Koch (Long Beach Bike Fit)

What is Ultimately Best for You

What’s the right length for you? Well, shorter might indeed be better but ultimately, a good bike fitter will be able to dynamically show you how different crank arm lengths can impact your pedal stroke yielding the most power, efficiency, and comfort.